The present invention relates to a hydro/aero-power generation plant and method for generating hydro/aero-power, and more particularly, to a tower for generating power by spraying water into the top of the tower to produce a downdraft of air that turns a turbine arrangement within the bottom of the tower to generate power.
The demand for power is increasing dramatically with expanding industrialization and the escalating use of high technology. The available natural resources, however, are continually being consumed and will eventually be used up. Other sources of power, such as nuclear plants, are in disfavor because of environmental concerns over the disposal of the resulting waste and possible accidents and wrong doings. Fossil fuel which is burned in thermal power stations involves air pollution, in general, and CO2 which causes warming of the atmosphere, in particular. There is a danger that the environment will be destroyed long before the fossil fuel will be used up. The effect of warming up the atmosphere is already a measurable phenomenon causing an increasing concern. On the other hand, estimates of the benefit of using clean renewable energy vary between 2 and 9 U.S. cents per kWh. Thus, there is a demand for a source of energy utilizing a renewable natural resource without the environmental damages.
The most common sources of energy employing renewable natural resources are hydroelectric plants, windmills and the burning of biomass. Hydroelectric plants plus the burning of biomass account for about 20% of the power produced in the world. It is unlikely, however, that the use of hydroelectric plants will significantly increase since the remaining sources are not readily exploitable and are not large in extent compared to those which have already been exploited. Similarly, energy produced by windmills is rather insubstantial on a world scale and has limited application. Several other renewable energy sources, such as Ocean Thermal Energy Conversion (OTEC), will not provide the necessary capacity or a low enough cost. The above mentioned renewable energy sources are not only limited in their capacity, but they are localized in certain small regions of the globe. Therefore, the need for an energy source using a renewable natural resource has largely gone unanswered.
One such source of energy utilizing a renewable resource exists in the geothermal, meteorological cycles of the earth. On a simplified global scale, the main cycle involves the sun heating the land, warming the air above and causing the air to rise. As the less dense warm air rises, a low pressure area is created which is filled by cooler, denser air from over the oceans. Thus, a natural convection occurs by the air flowing from the ocean to the land, rising above the land after being heated, and then falling over the ocean after being cooled. One of the most important geothermal cycles is the Hadley Cell named after its discoverer in 1735. Hot and humid air rises around the equator, then it expands and cools down. As a result of this action, rain is shed. The air then flows north and south around the globe. The air then descends mostly between 15xc2x0 and 35xc2x0 latitude, and turns back to the equator, while it collects moisture from the oceans, to replace the rising air. The descending air compresses adiabatically and warms up without regaining moisture, thus becoming hot and dry.
It is this descending air that produces the two belts of deserts around the globe. Clearly, hydro-electric power, wind energy and waves are also the result of the global geothermal cycles, however, the focus of the following is on utilizing another component of this cycle. The hot and dry air when cooled by a water spray will descend at an enhanced speed. This phenomenon occurs occasionally in nature and has been observed and recorded for a long time. In recent decades, it has been extensively studied because of its danger to aviation. It is sometimes called wind shear.
Some inventors have attempted to harness the geothermal energy in the atmosphere based on this simple and well-known principle that air can be cooled by spraying water into the air. Cool, moist air has a greater density than warm, dry air, and thus tends to fall toward the ground. For centuries, man has witnessed this phenomenon as a cloud burst on a hot summer day produces high winds and cools the area near the shower.
U.S. Pat. No. 3,894,393 to Carlson (the Carlson patent) suggested harnessing this power by initiating a downdraft of air within a duct by spraying water at a high elevation into the duct and extracting energy from the downdraft with a turbine near the outlet. There are several shortcomings in the Carlson patent, however, that appear to render the teachings impractical.
For example, the Carlson patent explains the physics and calculates the amount of water needed to be sprayed into the air at the top or at various elevations within the duct. According to the Carlson patent, the amount of water required is exactly equal to the amount that is evaporated to cool the air by xcex94T (column 5, lines 35-40), where it appears xcex94T is the average potential temperature difference, or cooling, between the inside and outside air (as it becomes clear from the equation on line 65). The average potential cooling, however, is less than the maximum cooling over the full height of the duct which occurs at the bottom of the duct. If only the suggested amount of water is used, optimal power output will never be reached. Also, spraying the suggested mass using sea water would appear to cause huge amounts of salt precipitation that will be difficult to handle.
The present invention, unlike Carlson, teaches that the maximum cooling depends on the amount of water spray and the droplet sizes, so that a maximum net power will be obtained. For a simplified explanation, the air outside the duct is assumed to follow the dry adiabatic process where the air is warmed due to compression about 1xc2x0 C. for every 100 meter drop in elevation. On the other hand, the air inside the duct theoretically can be immediately cooled by saturation. And then, upon being lowered and continuously wetted to saturation, the inside air is warmed about 0.5xc2x0 C. for every 100 meter drop in elevation following the wet adiabatic process. As uniquely shown by this invention, the air, as it falls inside the duct, can be further cooled by evaporation of more water keeping the air temperature as close as possible to the wet adiabat. Thus, an amount of water sufficient only for the average potential cooling as defined by the Carlson patent reduces the effective cooling or the effective height of the duct thereby providing only a fraction of the maximum potential cooling taught by the present invention.
Additionally, the Carlson patent does not appear to realize that the cooling within the duct takes place gradually rather than immediately, thereby further reducing the effective cooling or effective height of the duct. Thus, the average actual cooling mentioned by Carlson as the yardstick to determine the necessary amount of water spray is less than the average potential cooling and, therefore, the amount of water to be sprayed as suggested by Carlson is significantly less than the amount needed to achieve maximum potential cooling.
Further, the Carlson patent does not appear to recognize that a mass of water larger than theoretically will evaporate must be sprayed, as taught by the present invention disclosed herein. As the water droplets diminish by evaporation, the concentration of solutes increases, which decreases the vapor pressure at the surface of the droplet. The evaporation rate then decreases due to the decrease in the difference between the vapor pressure at the surface of a droplet and the vapor pressure of the air. Thus, unlike Carlson, the present invention teaches that a substantial amount of excess water must be sprayed into the duct to ensure the proper vapor pressure drive and rate of vapor and heat transfer to evaporate water within the duct and thereby achieve the maximum potential cooling.
Another shortcoming in the Carlson patent is the suggestion to make the droplet diameter very small to promote reaching maximum air density inside the duct as quickly as possible (column 6, lines 35-48). There are at least two negative consequences to this approach. First, reducing the diameter of the sprayed droplets dramatically increases the energy required to spray the water. Depending on the size of the droplets, the energy expended may outweigh the energy produced within the duct. Second, use of smaller droplets increases the costs of preventing the drift of the water and air mixture that exits the outlet. These costs may be high, as the water/air mixture exiting the duct typically contains solutes, like salt, that have negative environmental impact.
Besides these negative consequences, the Carlson patent does not appear to realize that, according to the present invention, increasing the amount of water sprayed, is in some ways just as effective in increasing the net power as the spraying of smaller droplets. Both ways, increasing the overall water spray and reducing the droplet size, require higher energy investment that may render the benefits of the energy tower economically non-feasible.
Still another problem is that the formula for the calculation of power, as disclosed in the Carlson patent, does not appear to properly take into account the vertical distribution of temperature, density, degree of evaporation and air velocity. Further, the Carlson patent does not appear to take into account the energy loss coefficient that is required to compute the net power output.
Yet another deficiency of the Carlson patent is that the recommended amount of sprayed water can be easily evaporated, leading to the precipitation of solutes. In using both sea water and fresh water, assuming the fresh water is not distilled, the evaporation of the water will cause the solution to reach a concentration that will cause poorly soluble solutes as well as common salt to precipitate. This will pose a tremendous problem for the equipment and in trying to dispose of the precipitated solutes.
A final problem with the Carlson patent, unlike the present invention, is that it does not appear to appreciate the full energy that can be generated by spraying excess water based on the hydro-drag effect. That is, water that does not evaporate transmits its momentum as well as its gravitational energy to the air within the duct. By locating the duct at an angle on the side of a hill, the Carlson patent does not appear to take advantage of this energy source.
Another system for generating electricity in an arid environment is disclosed in U.S. Pat. No. 4,801,811 to Assaf et al. (the ""811 patent). The ""811 patent, however, also has a number of drawbacks. By asserting that the maximum velocity within a duct is unrelated to the exit area (see e.g., column 2, lines 14-18 and column 1, lines 40-41), the ""811 patent appears to contradict both the laws of conservation of mass as well as the conservation of energy. Further, in equation 1 of the ""811 patent the pressure drop over the turbines is assumed to fully utilize the air head as if in a static state with no flow, no kinetic energy component and no energy losses. In equation 2, on the other hand, the velocity head used assumes the whole head of the air turns into a velocity head or kinetic pressure, as if there is no pressure drop over the turbines and no energy loss of any kind. The power is then calculated by multiplying the two: the velocity as if the whole head is turned into kinetic energy by the pressure drop as if the same head is turned fully to a pressure difference. This use of the same energy twice, with the addition of other mistakes, leads to an unattainably high power calculation.
Similar to the Carlson patent, the ""811 patent also does not appear to take into account the need for, or advantage of, spraying excess water. The ""811 patent states that the amount of water sprayed should equal the amount of water needed to saturate the air (e.g., column 5, lines 53-57). From the example given (e.g., column 5 line 60 to column 6, line 2), the intent appears to be that the saturation is to bring the air to the wet bulb temperature at the top inlet. As stated above, this results in numerous deficiencies that are even worse than those in the Carlson patent.
The recommendation of increasing the amount of water sprayed by 20% when using sea water (column 6, lines 33-51) does not cure these deficiencies. This increase still only provides about 70% of the optimal amount of spray water, resulting in a significant loss of power.
Also similar to the Carlson patent, the ""811 patent does not appear to take into account the full energy that can be generated by spraying excess water based on the hydro-drag effect. Besides strictly asserting that only the amount of water needed to saturate the air should be sprayed, this reference discloses systems in canyons and on the slopes of mountains that would prohibit utilizing the hydro-drag effect.
Further, the ""811 patent discloses that the size of the sprayed droplets should be less than about 100 microns in diameter (e.g., column 9, lines 32-38; column 8, lines 39-43; and column 6, lines 10-16). As mentioned above, producing water droplets of such a small diameter requires a significant energy investment. Since this reference suggests that the droplets should not exceed about 100 microns diameter, the average droplet diameter will be much less and thus the required energy will be even higher. The anticipated water head for spraying will be in the order of 1000 m (100 bars) or more, depending to a great extent on the droplet diameter distribution of the atomizer. Thus, the whole installation will be energetically useless or very marginal at best.
The ""811 patent also does not appear to fully appreciate the manner in which friction losses affect the output. In evaluating some calculations in the Carlson patent, the ""811 patent states that the friction losses would be so great that no useful work would result (e.g., column 1, lines 56-57). This evaluation appears to be incorrect because, regardless of the size of the friction coefficient, there will be some useful energy left if the installation is properly structured as discussed below. This is because the losses associated with such high Reynolds numbers under which the installation works increase very nearly in proportion to the velocity head, and if the coefficient is higher, the air velocity will be lower, but never zero. As long as there is a positive net energy, net energy being the gross mechanical energy minus the pumping energy, the system can be designed such that there will always be a net deliverable energy regardless of the energy loss coefficient. The only case where there will be no net deliverable energy is if the pumping and spraying energy exceeds the produced power. If there is a net mechanical energy after subtracting the pumping power, there will be a net deliverable power regardless of the friction coefficient. The net mechanical energy has to be divided into energy losses and energy directed to the turbines for useful deliverable work over and above pumping. This division can be optimized in order to get the maximum rate of deliverable energy production from the system. Carlson discusses the possibility of dividing the net mechanical energy in such a way, but does not appear to recognize and prove the optimum and how it can be used to compute the whole system and determine its embodiment. In summary, the ""811 patent does not contain any useful additions to Carlson""swork.
U.S. Pat. No. 4,742,682 (""682 patent) by Assaf et al., in addition to the ""811 patents discloses a heat exchanger which sprays warm brine into a tower to induce a downdraft that results in the cooling of the water and the production of energy. The ""8111 patent, the ""682 reference also incorrectly utilizes the full head for the pressure difference across the turbines and, again, the same head for the velocity head.
Further, the ""682 patent appears to misjudge the required spraying head for producing droplets of a radius of 1 mm, stating the required head is 3 cm (e.g., column 5, lines 38-41). The ""682 reference, in column 5, lines 42-45, states that xe2x80x9cas long as the droplet radius exceeds 0.1 mm, the surface energy and thus the energy required to create the droplets is quite smallxe2x80x9d. In reality, the energy required to produce droplets of this diameter using real atomizers with practical flow rates is hundreds of times greater than stated.
The feasibility of the design disclosed in the ""682 patent is questionable since the suggested tower height is merely 10 meters. The stated purpose of the invention is to recover some of the energy in pumping condenser water to a cooling tower that is 10 meters high. Yet, by suggesting spraying droplets of such small diameter, the pumping head will be increased to about 1000 meters or more, and the spraying energy cannot possibly be recovered when the whole tower is only 10 meters high.
Also, as discussed above, this reference results in problems in collecting the air/water mixture that exits from the cooling tower because of the small droplet size. The disclosed collection plates (e.g. column 6, lines 40-45) would appear to be ineffective since water droplets of such small diameter will tend to follow the air streamlines and flow around the plates.
A further deficiency in the ""682 reference is that it appears to be limited to high mixing ratios of water to air. In two examples, the reference discloses spraying 1 kg water per 1 kg of air and also 0.6 kg of water per 1 kg of air, whereas the preferred upper limit of water sprayed by the present invention is in the range not exceeding about 50 grams of water per kilogram of air.
Finally, the ""682 patent deals with water that is heated up in a heat exchanger before being sprayed. Notably, such preliminary warming significantly reduces the net energy which is produced by the down-flowing air. In the present invention, the heat quantity added in the sprayed water does not exceed 6,000 Joules/kg air, even when the main effect is the hydro-drag effect.
The ""682 patent appears to describe an inefficient cooling tower, certainly not an energy saving installation. For example, with a water/air ratio in the range of 0.5 kg/1 kg to 1 kg/1 kg and a water temperature just 10xc2x0 C. greater than the air temperature, the heat added to the air is 21,000 to 42,000 Joules/kg of air. The dry air, which typically can potentially evaporate 5 grams of water per kg of air (cooling the air by about 12.5xc2x0 C., characteristic of desert air) contains only about 12,000 Joules/kg cooling capacity. Thus, the cooling capacity of the air is much less than the heat which is intended to be extracted from the water spray.
U.S Pat. No. 5,284,628 to Pruiett (the Pruiett patent) discloses a convection tower for cleaning pollution from large quantities of air by spraying water into the air at the top of a tower, where the spray precipitates out the pollutants and the evaporation of the water creates a wind that can be used to turn turbines and generate electricity. This reference, however, does not appear to disclose a device that can fulfill the two goals of air cleaning and energy production because, for example, if the tower is low enough to capture dirty air then it is not high enough to feasibly generate energy.
Polluted air is usually an inversion layer which has been humidified and cooled and is thus heavier than the air above it. In order to produce a significant pressure difference across the turbines at the bottom of the tower to generate electricity, there must be a significant pressure differential between the air inside the tower and the air outside the tower which calls for further humidification and cooling and a significant height of a cooling duct. If the tower disclosed in the Pruiett patent is drawing polluted air, then there is not much ability to further cool and saturate the already cool and humid air in the duct. Thus, the Pruiett tower appears to be ineffective at generating energy if it must fulfill its cleaning task.
Further, if the Pruiett tower is made high enough to make the generation of energy practical, then it will no longer function as an air cleaning device since the top of the tower will be above the polluted inversion layer. Thus, the two stated objects of this invention are entirely conflicting goals.
Even if the aims of the Pruiett patent would not have been conflicting in the sense that tall towers will capture no dirty air and low towers will not produce energy, they would be conflicting in another sense. High efficiency in cleaning large volumes of air would call for maximum air flow and maximum air velocity. On the other hand, a maximum power output would require a highly moderated air flow and a compromise between the pressure drop across the turbines and the energy losses due to high kinetic energy. In effect, the optimal rate of air cleaning is obtained at negative net deliverable power, where even the pumping energy is not compensated.
The optimal air velocity is explained in the following. In any case, one aim almost excludes a practical application of the other. Other than the combination with air cleaning, the Pruiett ""628 patent adds nothing of practical or feasible value. It is suggested that in addition to air cleaning and power production, there will be a connected duct in which the humidified air will rise and the condensed water droplets will be collected as desalinated water. There are several grave deficiencies in this suggestion. The net power left for power production and air cleaning would become very small and possibly vanish completely, depending on the elevation difference between the down-flowing duct and the up-flowing duct. The amount of theoretically condensable water equals the moisture added due to the adiabatically warmed air on the way down. It is about 0.5xc2x0 C. for 100 m and accordingly less than one quarter gram water/kg air/100 m. If, for example, the primary shaft is 1,000 m high and 400 m in diameter, and the second shaft is 700 m and the average cooling is about 10 centigrade, then the maximum rate of air flow is about 12.5 m/sec. Even assuming 100% collection of condensed water (which is absolutely impossible to attain, even closely), the rate of the distilled water production is 3.2 grams/m2 cross section /sec. For a 400 m diameter duct, this amounts to a nearly 0.4 m3/sec for the whole cross-section.
This example would result in zero deliverable power and no air cleaning and would produce, at the maximum, not more than 400 liters water/sec. The pumping power alone would be of the order of at least 130 MW. This means an energy investment of about 90 kWh/m3 desalinated water. In comparison, sea water can be desalinated by reverse osmosis using a mere 4-5 kwh per cubic meter of desalinated water. Thus, to construct a 1,000 mxc3x97400 m main shaft and a twin tower of 700 m would require an investment which is at least an order of magnitude larger than the investment necessary for a conventional desalination plant of the same capacity and 20 times the energy outlay.
It is an object of the present invention to maximize the net deliverable power available through evaporative cooling.
A further object is to fully utilize momentum and the gravitational energy of unevaporated water droplets to produce energy.
Another object of the invention is to combine the effects of evaporative cooling and momentum and gravitational energy of unevaporated water droplets to optimize the net energy production.
Another object of this invention is to provide for a built-in energy pumped storage.
Yet another object is to desalinate water in a way which is more cost effective than present methods.
A further object is to intercept and reduce the volume of saline water that needs to be disposed, and to prevent salinization of fresh water sources.
Another object of the present invention is to enhance aquaculture.
Another object of the present invention is to enable the cooling of inland thermal power stations and utilize the waste heat of such stations.
A renewable resource power generation plant according to the present invention comprises a generally vertically extending duct having a side wall of a predetermined diameter, an inlet at a predetermined height and an outlet at an elevation lower than the inlet. A spray system is mounted adjacent the inlet for spraying droplets of a predetermined amount of water into the air, wherein a partial evaporation of the droplets causes the air to become cooler and denser than air outside the duct, creating a downdraft of air within the duct. A power system proximate the outlet recovers the energy from the downdraft of air.
One unique feature of the present invention is that the predetermined amount of water is greater than a calculable maximum amount of water that would theoretically evaporate in the air throughout substantially the entire predetermined height. Preferably, the ratio of the calculable maximum amount of water that would theoretically evaporate to the predetermined amount of sprayed water is in the range of about 0, when there is no cooling, to about no more than 0.9, if the main effect is the aero-cooling effect.
An advantageous result of adding liquid water to the downdraft is that the optimal net energy is produced because adding more water than can evaporate optimizes evaporative cooling and additionally generates energy in the power system through the recovered spray momentum and gravitational energy of the unevaporated water droplets. When there is an elevated water source, then gravitational energy is a primary source and a real addition to the net energy output. When the excess water needs to be pumped up to the spray system, the gravitational energy transmitted to the power system results in the recovery of most of this pumping energy.
Evaporative cooling is referred to as the aero-cooling effect wherein the water added to the air lowers the air temperature and increases the air density, thus creating a downdraft. The gravitational potential energy from the unevaporated droplets, and also some initial momentum of the sprayed droplets which is transmitted to the air in the duct, is referred to as the hydro-drag effect.
Adding liquid water to the air in the duct combines these effects to produce the maximum net deliverable power. Even when the air at the top inlet is saturated with vapor, there will still be some aero-cooling effect due to the adiabatic warming as the air descends and due to the presence of excess water.
The hydro-drag effect contribute to the primary energy when it uses an elevated water source. The hydro-drag effect can also be used as the main source of deliverable energy when the water must first be pumped up, as in the case of pumped storage. In the case where the hydro-drag effect is the main source of deliverable energy, the preferred rate of spray that would utilize fully the installed capacity of the plant is found to be up about 5 times the rate of spray used when the aero-cooling cooling effect is the main effect to obtain the same power.
Preferably, the total heat mass added to the air in the duct by the droplets of sprayed water is less than about 7,500 Joules per kg of air.
The predetermined height of the duct is generally greater than about 100 meters, and preferably greater than about 500 meters.
Also, the ratio of the predetermined height to the predetermined diameter is an advantageous feature in optimizing the performance of the power plant. For a power generation plant designed to have a fixed installed output, the predetermined height is preferably in the range of about 3 to 5.5 times greater than the predetermined diameter. For a power generation plant designed to have a fixed height, the predetermined height is preferably in the range of about 2 to 2.5 times greater than the predetermined diameter.
Another preferred feature of the present invention is that the inlet comprises a substantially horizontal flared portion curving radially out from the top of the side wall. The radius of curvature of the flared portion is preferably about 0.2 times the predetermined diameter. Alternatively, the second derivative of the flared portion is approximately continuous.
In a presently preferred embodiment of the tower construction the side wall includes an inner cylinder concentric with and structurally linked to an outer cylinder for structural stability enhancement. Further, the side wall may include at least one room defined by plumbing, electricity, and a ceiling and a floor disposed between the inner cylinder and the outer cylinder. This inner room can be utilized for needed services to the tower and for other functions, such as residential, commercial, hotel floor space, etc.
To promote the most efficient air flow, the inner surface of the inner cylinder in the preferred embodiment has a roughness less than about a few units in a million in relation to the predetermined diameter. The shape of the inner surface of the inner cylinder is also important in providing efficient air flow and in eliminating protrusions that will cause the falling droplets to become attached to the inner surface. The shape of the inner cylinder may be a cross-section of a circle, a polygon, a circle having circular sections bulging out and the intersection of two circular sections forming a sharp internal edge, a circle having circular sections alternating from bulging in to bulging out forming an undulating surface, and a circle having vertical radial ribs.
An advantageous feature of the present invention is the shape of the outer cylinder, which helps to reduce the structural load placed on the duct. The outer cylinder may be in the shape of stacked vertical discs having outer circular edges greater in diameter than inner circular edges, wherein said outer vertical edges are tied vertically and diagonally by tension elements. Alternatively, the outer cylinder may include an outer surface in the shape of a spiralling vertical serration having outer circular edges greater in diameter than inner circular edges, wherein said outer vertical edges are tied vertically and diagonally by tension elements.
The outlet of the duct also uniquely contributes to the efficiency of the power plant. The outlet comprises a flared portion curving radially out from the bottom of the side wall to form a diffuser region having a radially outward increasing vertical cross-sectional area which reduces the velocity of the outflowing air, wherein the ratio of the vertical cross-sectional area at the outermost point of the diffuser region to the cross-sectional area of the duct of a predetermined diameter is in the range of about 1:1 to 3:1. Preferably, the ratio is in the range of about 1.25:1 to 2.25:1 Also, the radial length of the turbine and diffuser region preferably extends the overall radius of the tower base by about 1/2 the predetermined diameter of the duct.
In accordance with another advantageous feature of the present invention, the water is preferably supplied from an elevated water source. This source can be a natural source of water or a plurality of elevated operational reservoirs capable of storing a volume of water that will allow a water spray distribution with time over a whole week not in conformity with the time distribution of pumping the reservoirs operating only in part of the hours over the week, preferably, when the return or delivered energy is low. A plurality of operational reservoirs may be advantageously mounted within the tower side wall and provide a supply of water lasting in the range of about minutes to fractions of an hour. This is in order to divide the pumping into serial elements and parallel elements, as well as providing other advantages.
The sprayed droplets may have an average diameter greater than about 100 microns, preferably in the range of about 150 to greater than 500 microns. The spray system provides a substantially uniform ratio of droplets to air across the entire cross-section of the duct. Local deviations in the droplet to air ratio are preferably less than about 10%.
The spray system can spray a volume of water ranging from about zero to the predetermined amount of water with an accuracy within about 1/30 of the predetermined maximum amount of water. Further, the spray system has a substantially redundant capacity, preferably greater than about 50%. The water atomizers should preferably be installed in a way that a large proportion of the spraying energy can be recovered. This is, in part, by directing the spray in such a way that the water velocity vector will be substantially parallel to the local air flow velocity vector.
The spray system may advantageously spray droplets having an electrical charge, wherein areas of the electrically charged droplets of one sign alternate with areas of electrically charged droplets of the opposite sign. Alternatively, areas of the electrically charged droplets may alternate with areas of droplets having no charge, the preferably electrical charge sign being positive. The power system may be adapted to attract the electrically charged droplets. The spray system may further include a secondary spraying system mounted at the perimeter of the duct, at any elevation but preferably near its bottom, for spraying droplets greater in diameter than the droplets from the spray system mounted adjacent the inlet. The secondary spray system droplets are preferably greater than about 300 microns in diameter. Further arrangements include main spray water near the inlet charged electrostatically by one sign and the secondary spraying system mounted at the perimeters of the duct charged electrostatically by the opposite sign. Another location of a secondary spraying system can be in the diffuser region, radially outward from the power system where more than one spray may be utilized having different charge signs and possibly using low salinity water.
The power system may further comprise a plurality of shrouded turbines for recovering the energy from the downdraft of air. The turbine blades form a close fit with the shroud so that air cannot circumvent the turbines. A unique feature of the present invention is that the amount of recovered energy is substantially maintained when a predetermined number of the plurality of turbines are closed to prevent airflow therethrough. Also, a select number of the plurality of turbines may directly power the supply of water to the spray system avoiding the need to produce electricity by the turbines and then use this electricity to motivate a motor that in turn moves the pump. To further maximize the efficiency of the power plant, the blades and/or guide vanes of the plurality of turbines may have adjustable pitch and the turbines may preferably be designed to work at least two fixed rotational speeds in accordance with the turbine head in order to achieve high efficiency.
The power generation plant may further comprise a collection area around the duct having ground preparations for inhibiting the absorption of unevaporated water droplets, carried in the downdraft of air exiting the outlet, into the ground and directing the droplets into a plurality of collection reservoirs. The ground preparation comprises at least two alternating layers of impermeable soils and impermeable membranes having seams, wherein the seams of one layer are laterally spaced apart from the seams of an adjacent layer. The collection reservoirs may uniquely supply the collected water back to the spray system when the sprayed water has lower initial solute concentration. Also, the collection reservoirs may supply the collected water to a disposal site and to an energy recovery system comprising hydroelectric turbines.
A synergistic combination of technologies results when adding a desalination system connected to the water supply and spray system wherein the predetermined amount of water may flow through the desalination system before reaching the spray system. Preferably, the desalination system utilizes the reverse osmosis method. Alternatively, only a fraction of the predetermined amount of water may flow through the desalination system.
Another unique synergistic combination results when adding an aquaculture farm connected to the water supply system wherein the predetermined amount of water may flow through the aquaculture farm before reaching the spray system. Alternatively, similar to the desalination system, only a fraction of the predetermined amount of water may flow through the aquaculture farm.
Another unique feature of the present invention is that preferably 1/3 of the net energy is used for energy losses due to the air flow and 2/3 of the net energy is turned into the turbines to produce a net deliverable power, the net energy being defined as the potential energy due to the increased air density under static conditions minus the energy required for pumping and spraying the water. The division of 1/3 and 2/3 is approximate, but with only small deviations as will be explained below.
A renewable resource power generation plant according to the present invention also comprises a downdraft of air driven by the evaporation of the water droplets causing the aero-cooling effect and the spray and gravitational energy of the excess water falling within the duct causing the hydro-drag effect.
Also disclosed is a method for generating power, comprising the steps of isolating a column of air from the surrounding air, wherein one end of the column of air is at a greater elevation than the other end; adding a predetermined amount of water to the air column to maximize the cooling and density of the air at every elevation throughout the air column, thereby causing a flow of air down the column; and recovering energy from the air flow at the lower end of the air column. In adding the water, the predetermined amount of water is preferably in the range of about 1.1 to over 2.5 times a calculable maximum amount of water that would theoretically evaporate at every elevation throughout the air column. This is when the main power source is due to the aero-cooling effect.
The unevaporated water droplets resulting from adding more than the calculable maximum amount of water that would theoretically evaporate may be collected. These unevaporated droplets have a greater concentration of solutes than the water added to the air column. Additionally the collected droplets can be recycled, until a predetermined solute concentration level is reached, by adding a predetermined amount of collected droplets to the air column to increase the cooling and density of the air at every elevation throughout the air column thereby causing a flow of air down the column.
Further, the collected droplets that have reached the predetermined solute concentration level may be disposed by introducing the collected droplets into a water source where the collected droplets are gradually diluted over time. Preferably, the collected droplets are introduced at a low velocity at a water depth having a similar density to the density of the collected droplets.
A method of disposing of a solution containing environmentally harmful concentrations of solutes is also disclosed, comprising the step of introducing the solution into a body of water where the solution is gradually diluted over time. Preferably, the solution is introduced at a low velocity at a water depth having a similar density to the density of the solution. The above method of disposing the concentrated brine into the water depths also makes it possible to load into the water different pollutants such as organic refuse from fish growing, sewage, sludge, etc. This will delay and dilute the effect of such pollutants. The increased concentration of this water and its reduced volume can also be utilized in disposing of solutes that would otherwise salinize fresh water resources.
Still other objects and advantages of the present invention will become readily apparent to those skilled in this art from the following detailed description, wherein only the preferred embodiments of the invention are shown and described, simply by way of illustration of the best mode contemplated of carrying out the invention. As will be realized, the invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the invention. Accordingly, the drawing and description are to be regarded as illustrative in nature, and not as restrictive.